DESCRIPTION: The sympathetic nervous system (SNS) plays an important role in regulating the immune system. Cellular adhesion molecules (CAMs) are cell-surface receptors and ligands responsible for mediating intercellular interactions, including adhesion of leukocytes to the vascular endothelium. They are highly relevant to studies of cardiovascular disease. In pilot work the investigators have observed that behavioral and exercise stressors have significant effects on CAMs and that these effects are different in individuals with hypertension. This study will pursue these observations by determining the effects of sympathetic nervous system activation on CAMs. The investigators will study 40 hypertensive and 40 normotensive men and women on placebo and on a non-specific beta-adrenergic receptor blocker in a double blind crossover experiment. CAMs, plasma catecholamines, blood pressure, heart rate and total peripheral resistance will be measured at rest and in response to three different sympathetic nervous system stimuli: a behavioral stressor, an exercise stressor, and a beta-adrenergic agonist fusion. Lymphocyte beta(2)-adrenergic receptor density and sensitivity will also be determined. CAMs will be examined both in terms of number (in vivo expression on peripheral cells) and function (in vitro CAM-mediated lymphocyte transendothelial migration). The project will help elucidate the effects of sympathetic activation on CAMs and the degree to which this physiology is altered in individuals with hypertensive disease.